Ideally, a controllable RF phase shifter should have minimum size, minimum insertion loss, minimum weight, minimum cost and complexity, substantial immunity from all adverse ambient environmental factors (including physical and electrical) and an ability to produce any desired phase shift accurately and instantly upon demand. Unfortunately, in spite of many years of effort by those in the art, the truly ideal phase shifter has yet to be realized.
A waveguide mode twin slab ferrite phase shifter (e.g. of the type described in commonly assigned U.S. Pat. No. 4,445,098--Sharon et al.) is one of the most accurate phase shifters known to date. However, in prior realizations. Such waveguide mode phase shifters are large and expensive. If unswitched reciprocity is desired, this waveguide unit used in conjunction with circulators is too large for two dimensional phased arrays (where inter-radiator dimensions on the order of 0.6 wavelength are involved).
The Sharon et al. type of dual toroid ferrite phase shifter has been greatly miniaturized and incorporated serially with a microstrip transmission line to produce a novel, ultra-miniaturized, essentially planar, phase shifter of superior structure and performance. A miniaturized dual toroid phase shifter is disclosed in the application entitled "Hybrid Mode Phase Shifter" identified above.
There has been a need for a miniaturized single toroid phase shifter. Accordingly, we have successfully converted the miniaturized dual toroid phase shifter into a single toroid phase shifter Some of the advantages that the single toroid phase shifter has over the dual toroid phase shifter are that it is less complex, more economical to produce and more compact.
The present invention may, in some respects, be described as a single toroid, side slab miniaturized waveguide phase shifter inserted serially between interrupted matched-impedance microstrip transmission lines. Some embodiments may position the waveguide portion into an underlying ground plane structure while others dispose at least a portion of the waveguide above the top level of a microstrip substrate. In a presently preferred embodiment, the waveguide portion is butted between terminated ends of the microstrip substrate so that the maximum thickness of the whole device is merely that of the central waveguide portion.